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Using Text Components

Using Text Components. JTextComponent. JTextArea. Plain Text Areas. JTextTextField. JEditorPane. JPasswordField. JTextPane. Text Controls. Styled Text Areas. Text Controls. Also called text fields Can display and edit one line of text at a time

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Using Text Components

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  1. Using Text Components JTextComponent JTextArea Plain Text Areas JTextTextField JEditorPane JPasswordField JTextPane Text Controls Styled Text Areas

  2. Text Controls • Also called text fields • Can display and edit one line of text at a time • Respond to action events, typically the user typing the Enter key • Used to get a small amount of textual information from the user • JPasswordField is an extension of JTextField that does not display typed text

  3. Text Field Example • Display a labeled text field with the following behavior: • User enters text followed by the Enter key • If the entered text is not ''quit'', the text is highlighted (selected) and then nothing is done • Subsequent typing in the field will cause the highlighted text to be erased • If the entered text is ''quit'', the program exits

  4. Display After the user enters some text and hits Enter:

  5. Text Field Code ... JLabel label = new JLabel("Enter a command:"); JTextField textField = new JTextField(20); textField.setPreferredSize(new Dimension(50,20)); textField.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { String command = textField.getText(); if (command.equals("quit")) { frame.dispose(); // frame is top-level System.exit(0); // JFrame } else { textField.selectAll(); } } }); JPanel panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); panel.add(label); panel.add(textField); frame.getContentPane().add(panel); frame.setVisible(true); ...

  6. Notes On The Code • The argument to the JTextField constructor is a preferred size for the visible area; the length of the string entered is not limited • As with buttons, text fields are action-based • The action listener is created using a constructor for an anonymous class that extends the action listener interface • The getText method returns the entered string • The selectAll method highlights the string • The label and text field are put into a JPanel first; otherwise the text field would fill the frame

  7. Plain Text Areas • JTextArea can display and edit multiple lines of text • Text can be displayed in any font, but all of the text is in the same font • Use a text area to allow the user to enter unformatted text of any length • Also can be used to display unformatted help information

  8. JTextArea Example ... JTextArea textArea = new JTextArea( "This is an editable JTextArea " + "that has been initialized with the setText method. " + "A text area is a \"plain\" text component, " + "which means that although it can display text " + "in any font, all of the text is in the same font." ); textArea.setFont(new Font("Serif", Font.ITALIC, 16)); textArea.setLineWrap(true); textArea.setWrapStyleWord(true); JPanel panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); panel.add(textArea); frame.getContentPane().add(panel); // frame is the top-level frame.setVisible(true); // JFrame ...

  9. Example Display Note that a default text area width was used, and that the text does not fit in the frame. It needs to have its text displayed within a scroll pane.

  10. JTextArea Example Modified textArea = new JTextArea( "This is an editable JTextArea " + "that has been initialized with the setText method. " + "A text area is a \"plain\" text component, " + "which means that although it can display text " + "in any font, all of the text is in the same font." ); textArea.setFont(new Font("Serif", Font.ITALIC, 16)); textArea.setLineWrap(true); textArea.setWrapStyleWord(true); JScrollPane areaScrollPane = new JScrollPane(textArea); areaScrollPane.setVerticalScrollBarPolicy( JScrollPane.VERTICAL_SCROLLBAR_ALWAYS); areaScrollPane.setPreferredSize(new Dimension(200, 150)); panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); panel.add(areaScrollPane); frame.getContentPane().add(panel); frame.setVisible(true);

  11. New Display

  12. Styled Text Areas • JEditorPane and JTextPane objects can display text in multiple fonts • Some allow embedded images and even embedded components • Require more up-front programming to set up and use • Exception: JEditorPane can be easily used to display formatted text from a URL

  13. Digression: The Model-View Approach to Software Architecture • Like most Swing components, the text components use a model-view approach • The model is the data about the underlying component • The view is a presentation of the data • E.g., underlying a JButton is a ButtonModel object that has: • whether it is enabled • whether it is selected • whether it is pressed • what its keyboard mnemonic is

  14. The Model-View Approach to Software Architecture (cont'd) • Why separate the model from its view? • So that different Look-and-Feels can be created for the same data • If you need the data for some processing, it is much more efficient to get it directly from the model than from the component that is presenting it • All JTextComponent classes provide views of their associated models, called documents

  15. Documents • Each document is an instance of a class that implements the Document interface • A document must provide the following services for a text component: • Contain the text • Provide support for text editing • Notify listeners of changes to the text • Manage a position within the text • Allow retrieval of information like text length, and of sub-portions of the text

  16. Document Class and Interface Hierarchy AbstractDocument Document implements implements PlainDocument DefaultStyledDocument StyledDocument implements Used by JTextField and JTextArea Used by JTextPane HTMLDocument Used by JEditorPane

  17. The JEditorPane Class • JEditorPane is the foundation for Swing's styled text components • A JEditorPane object becomes an editor for the type of content it is given: • text/plain: plain text • text/html: Hypertext Markup Language • text/rtf: Rich Text Format • Uses an instance of the EditorKit class to accomplish editing tasks • Can be used to display uneditable URLs

  18. Loading Content into a JEditorPane • setText: initializes the component from a String • read: initializes the component from a Reader • setPage: initializes the component from a URL • Besides using these methods, similar loading can be accomplished using constructors

  19. JEditorPane Example JFrame frame = ... // make top-level window editorPane = new JEditorPane( "text/plain", "Here is a string of text\n" + "initialized in the constructor.\n" + "Note that we gave the type\n" + "\"text/plain\" as the first argument."); JScrollPane editorScrollPane = new JScrollPane(editorPane); editorScrollPane.setVerticalScrollBarPolicy( JScrollPane.VERTICAL_SCROLLBAR_ALWAYS); editorScrollPane.setPreferredSize(new Dimension(300, 300)); JPanel panel = ... // make panel to hold editorPane and // add panel to frame

  20. Example Display

  21. Loading From URLs • Consider the following HTML file, called Test.html: <html> <head> <title>A Test HTML Page</title> </head> <body> <h1>A Test HTML Page</h1> <center> <table border> <tr><th> Fruits <th> Vegetables <th> Drinks </tr> <tr><td> Apples <td> Broccoli <td> Milk </tr> <tr><td> Bananas <td> Spinach <td> Juice </tr> <tr><td> Oranges <td> Carrots <td> Soda </tr> <tr><td> Grapes <td> Squash <td> </tr> <tr><td> Lemons <td> <td> </tr> </table> </center> </body> </html>

  22. Loading From URLs (cont'd) • A file URL is of the form: • file:<directory><separator><filename> • There is a URL class constructor that takes a string representing a file URL specification as an argument • We could code the specification directly: • new URL(''file:/home/cs/tcolburn.../Test.html'') • Or we can use the System class to build the specification

  23. System Class Properties • Java maintains a list of system properties and their values, implemented as a hash table. Some of them: PropertyValue os.name Operating system name os.arch Operating system architecture os.version Operating system version file.separator ''/'' on Unix path.separator '':'' on Unix line.separator ''\n'' on Unix user.name User's account name user.home User's home directory user.dir User's current working directory Use Sytem.getProperty(''<property>'') to retrieve a value

  24. Example That Loads A File URL import java.io.*; import java.net.*; ... editorPane = new JEditorPane(); editorPane.setEditable(false); try { url = new URL("file:" + System.getProperty("user.dir") + System.getProperty("file.separator") + "Test.html"); editorPane.setPage(url); } catch (IOException e) { System.err.println("Attempted to read a bad URL: " + url); } catch (Exception e) { System.err.println("Couldn't create URL: " + url); } JScrollPane editorScrollPane = new JScrollPane(editorPane); ... panel = new JPanel(); ... panel.add(editorScrollPane); frame.getContentPane().add(panel); frame.setVisible(true); ...

  25. Notes On The Example • The URL class is in the java.net package • setEditable(false) is used to keep the HTML document from being edited • new URL(...) can throw an exception if the file URL specification is malformed • setPage(url) can throw an exception if the URL argument cannot be read for some reason

  26. Example Output

  27. Example That Loads A Network URL import java.io.*; import java.net.*; ... editorPane = new JEditorPane(); editorPane.setEditable(false); try { url = new URL("http://www.d.umn.edu/~tcolburn/hours.html"); editorPane.setPage(url); } catch (IOException e) { System.err.println("Attempted to read a bad URL: " + url); } catch (Exception e) { System.err.println("Couldn't create URL: " + url); } JScrollPane editorScrollPane = new JScrollPane(editorPane); ... panel = new JPanel(); ... panel.add(editorScrollPane); frame.getContentPane().add(panel); frame.setVisible(true); ...

  28. Example Output

  29. The JTextPane Class • The JTextPane class extends JEditorPane • A text pane inherits the capabilities of an editor pane but insists that its document be a styled document • You can embed images and components in a text pane • You can embed images in an editor pane too, but only by including them in an HTML or RTF file

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